The present invention relates to an air damper, and in particular, relates to an air damper for generating a damping force when a piston moves in one direction.
Conventionally, an air damper is used, for example, in an automobile glove compartment in order to obtain high quality when a cover thereof opens. Such an air damper has a cylinder having a cylindrical shape with a bottom, and a piston disposed inside the cylinder to move freely back and forth coaxially. A piston rod which is integrally formed with the piston projects toward a side opposite to the bottom part of the cylinder.
Patent Document 1: Japanese Patent Publication (Kokai) No. 08-105482
In the air damper described above, a cylinder opening in a projecting direction of the piston rod is closed with a cap. The piston divides the cylinder into two air chambers between the cylinder bottom and the cap, and the piston is provided with an orifice and an O-ring. A recess portion and a groove are formed for allowing the O-ring to move in an axial direction of the piston. When a cover opens and the O-ring moves, the groove is closed and air moves between the two chambers via the orifice. When the cover is closed and the O-ring moves, air moves between the two chambers via the groove. Accordingly, it is possible to provide an air damper in which damper effect is obtained through the orifice when the cover opens, and resistance becomes small due to air passing through the groove when the cover is closed.
In the air damper having the structure described above, a thickness of the piston in the axial direction (portion for moving the O-ring) becomes large to a certain extent. When the piston is molded using a synthetic resin material, a recess portion is provided on an end surface of the piston in order to prevent sink or deformation of a thick part. In this case, air pocket is formed in the recess portion between the bottom of the cylinder and the end surface of the piston, and air inside the pocket temporarily expands when the cover opens. Accordingly, there may be a damper inactive zone (idling interval, idling distance), in which air resistance is not generated, and buffering force or damping force is not generated upon opening the cover.
The piston may be formed in a solid shape without the recess portion. In this case, sink or deformation may occur, thereby making it difficult to control a size and a shape.
In view of the problems described above, an object of the present invention is to provide an air damper with a piston made of a synthetic resin, in which a damper inactive zone due to an air pocket is eliminated while preventing sink or deformation of the piston.
Further objects and advantages of the invention will be apparent from the following description of the invention.